Modification of the Backbone Structure

This is in contrast to the situation with analogous ferrocene compounds, where the substitution of OH with nucleophiles under the same conditions proceeds 

Another possibility for creating a new ligand structure is to connect two phos-phaferrocene molecules via their formyl functional groups. The reductive coupling of carbonyl compounds with low-valent Ti reagents - the McMurry reaction - is a technique that has found wide application in organic synthesis [18]. 

The E and Z configurations were assigned by determining the Jhh coupling constant between the two chemically equivalent olefinic protons from the satellites in the H P NMR spectrum, and has been confirmed by X-ray analysis of both isomers [19], 

From a stereochemical point of view, the pinacol-type coupling is much more interesting, because two new stereogenic centers are established at the former carbonyl C atoms. When the coupling reactions described above were carried out with (R)-2 at 0 °C the pinacol product 19 (Fig. 1.5.4) was obtained as one out of three possible stereoisomers. 

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